U.S. patent application number 12/889750 was filed with the patent office on 2011-04-07 for battery pack.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Masaki Hogari, Atushi Nakanouchi.
Application Number | 20110080140 12/889750 |
Document ID | / |
Family ID | 43822696 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110080140 |
Kind Code |
A1 |
Hogari; Masaki ; et
al. |
April 7, 2011 |
BATTERY PACK
Abstract
A battery pack includes a current control device that has a
thermostat and a positive temperature coefficient device whose
resistance increases as the temperature rises connected in
parallel, the current control device being inserted into a
discharge current path of a battery cell and a protection circuit
that detects a voltage of the battery cell, detects an overcharge
and over-discharge of the battery cell, and generates an overcharge
detection signal and an over-discharge detection signal. In a
normal state, a discharge current of the battery cell flows through
the thermostat of the current control device. When the discharge
current is large enough to damage the battery cell, the thermostat
turns off and the discharge current flows through the positive
temperature coefficient device. When the positive temperature
coefficient device produces heat, a resistance of the positive
temperature coefficient device increases and the discharge current
is limited or interrupted.
Inventors: |
Hogari; Masaki; (Fukushima,
JP) ; Nakanouchi; Atushi; (Fukushima, JP) |
Assignee: |
SONY CORPORATION
Tokyo
JP
|
Family ID: |
43822696 |
Appl. No.: |
12/889750 |
Filed: |
September 24, 2010 |
Current U.S.
Class: |
320/134 |
Current CPC
Class: |
H01M 10/0525 20130101;
H01M 10/637 20150401; H01M 10/613 20150401; H01M 10/6235 20150401;
H01M 10/486 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
320/134 |
International
Class: |
H02J 7/04 20060101
H02J007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2009 |
JP |
P2009-229915 |
Claims
1. A battery pack comprising: a current control device that has a
thermostat and a positive temperature coefficient device whose
resistance increases as the temperature rises connected in
parallel, the current control device being inserted into a
discharge current path of a battery cell; and a protection circuit
that detects a voltage of the battery cell, detects an overcharge
and an over-discharge of the battery cell, and generates an
overcharge detection signal and an over-discharge detection signal;
wherein, in the current control device, a discharge current of the
battery cell flows through the thermostat in a normal state, the
thermostat turns off and the discharge current flows through the
positive temperature coefficient device when the discharge current
is large enough to damage the battery cell, and a resistance of the
positive temperature coefficient device increases and the discharge
current is limited or interrupted when the positive temperature
coefficient device produces heat.
2. The battery pack according to claim 1, wherein a supply terminal
for a charge current to the battery cell is disposed separately
from an output terminal for a discharge current from the battery
cell.
3. The battery pack according to claim 2, wherein a fuse for
interrupting an excessive charge current is connected between the
supply terminal for the charge current and the battery cell.
4. The battery pack according to claim 1, wherein a switching
device for protecting the battery cell from the overcharge and the
over-discharge is attached to each of a charging unit and an
application apparatus connected to the battery pack.
5. The battery pack according to claim 4, wherein the protection
circuit includes a communication means for performing communication
between the charging unit and the application apparatus, the
communication means for transmitting a signal for controlling the
switching device.
6. The battery pack according to claim 1 used as a power source for
a motor of a power tool.
7. The battery pack according to claim 1, wherein a regulator
forming a stable direct voltage from a voltage of the battery cell
is disposed.
8. The battery pack according to claim 1, further comprising a
microcomputer and a control IC, wherein the microcomputer normally
operates in a sleep state to save power consumption and shifts from
the sleep state to a normal operation state when receiving a signal
from the control IC.
9. The battery pack according to claim 4, further comprising a
microcomputer, a control IC, a first FET, a second FET, and third
FET, wherein the first FET, the second FET, and the third FET are
disposed as the switching device, the first FET being turned on by
an overcharge detection signal output by the control IC, the second
FET being turned on by an over-discharge detection signal output by
the control IC, and the third FET being turned on and off by the
microcomputer.
10. The battery pack according to claim 5, wherein the
communication unit performs certification between the battery pack
and the charging unit when the battery pack is connected to the
charging unit for charging.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority to Japanese Priority
Patent Application JP 2009-229915 filed in the Japan Patent Office
on Oct. 1, 2009, the entire content of which is hereby incorporated
by reference.
BACKGROUND
[0002] The present application relates to a battery pack applied to
a power source for power tools such as an electric drill, electric
screwdriver, and electric disc grinder.
[0003] A lithium ion secondary battery (referred to below as a
lithium ion battery as appropriate) that relies on doping and
undoping of lithium ions is used as a power source (secondary
battery) for power tools. The lithium ion battery has a positive
electrode obtained by forming, on a positive electrode collector, a
positive electrode active material layer that uses lithium
composite oxides such as LiCoO.sub.2 or LiNiO.sub.2 and a negative
electrode obtained by forming, on a negative electrode collector, a
negative electrode active material layer that uses carbonaceous
material such as graphite or non-graphitizable carbonaceous
material capable of being doped or undoped with lithium. The
positive electrode and negative electrode are laminated alternately
with a separator disposed therebetween and bent or wound to be used
as battery module. The battery module is housed in a metal can or
laminate film together with nonaqueous electrolyte obtained by
dissolving lithium salts in aprotic organic solvent to configure a
battery.
[0004] A protection circuit is necessary to prevent lithium ion
batteries from an overcharge, over-discharge, or overcurrent. Since
a power tool consumes a relatively large current, protective
devices with a high current capacity are necessary. However, FETs
(field effect transistor), fuses, and other protective devices with
a high current capacity are large in size and expensive. In
addition, fuses blow to protect batteries, but they become
unavailable again without being replaced.
[0005] Japanese Unexamined Patent Application Publication No.
2005-222834 proposes a switch that has an overcurrent protection
function in which a mechanical switch and a positive temperature
coefficient device (also referred to as a PTC thermistor) are
combined. The PTC device has a low resistance at a relatively low
temperature, but its resistance increases sharply above a certain
temperature.
SUMMARY
[0006] In consideration of the above-described characteristics of a
fuse, the current above which the fuse blows is likely to be set to
a large value. As a result, the characteristics of the fuse are
selected so that the fuse does not blow in the area where a lithium
ion secondary battery is overloaded and it blows during occurrence
of an overcurrent when, for example, the load is short-circuited.
Accordingly, a problem with this protection function is that the
security of a lithium ion secondary battery is not ensured
completely even when a fuse is installed.
[0007] When a lithium ion secondary battery is used as the power
source for power tools, it is likely that the current is controlled
by a switching device such as a FET in the operation area where low
or middle load is applied and direct connection to a load (for
example, a brushless motor) is performed via the open/close contact
by bypassing a switching device such as a FET in the operation area
where high load is applied when the maximum power is necessary. In
this type of configuration, when the load of an electric
screwdriver becomes excessively large during operation and the
motor stops turning, if the operator does not turn off the trigger
switch for energization, the overcurrent almost the same as in a
short-circuit of the coil continues flowing. As a result, the
lithium ion secondary battery suffers damage such as a breakage of
the lead electrode, a shrinkage of the separator, or a
short-circuit due to melting of the separator. As described above,
it is necessary for the user or operator to protect the lithium ion
secondary battery from being overloaded.
[0008] When the lithium ion secondary battery suffers damage
because the overcurrent almost the same as in a short-circuit of
the load flows during occurrence of a lock of the motor, another
method for ensuring the security is to detect damage (internal
short-circuit) the next time the battery is charged, and interrupt
charge current based on the detection. This method, however, may
not surely detect the damage of the lithium ion secondary battery,
so the protection of the battery becomes insufficient.
[0009] In the switch with the overcurrent protection function
proposed in Japanese Unexamined Patent Application Publication No.
2005-222834, the PTC device is connected to the switch in series so
that the PTC device can have a high resistance for overcurrent
protection when an overcurrent flows. However, when an overcurrent
is limited only by the PTC device, an overcurrent in power tools
may not be prevented and damage to the lithium ion secondary
battery may not be prevented reliably.
[0010] Accordingly, it is desirable to provide a battery pack in
which compact and recoverable current control devices are used to
reliably prevent damage to battery cells.
[0011] According to an embodiment, there is provided a current
control device inserted into a discharge current path of a battery
cell, the current control device having a thermostat and a positive
temperature coefficient device whose resistance increases as the
temperature rises, connected in parallel; a protection circuit that
detects a voltage of the battery cell, detects an overcharge and an
over-discharge of the battery cell, and generates an overcharge
detection signal and an over-discharge detection signal; in which,
in the current control device, a discharge current of the battery
cell flows through the thermostat in a normal state, the thermostat
turns off and the discharge current flows through the positive
temperature coefficient device when the discharge current is large
enough to damage the battery cell, and a resistance of the positive
temperature coefficient device increases and the discharge current
is limited or interrupted when the positive temperature coefficient
device produces heat.
[0012] Preferably, a supply terminal for a charge current to the
battery cell is disposed separately from an output terminal for a
discharge current from the battery cell. In this case, a fuse for
interrupting an excessive charge current is connected between the
supply terminal for a charge current and the battery cell.
[0013] A switching device for protecting the battery cell from the
overcharge and the over-discharge is attached to each of a charging
unit and an application apparatus connected to the battery pack. In
this case, the protection circuit includes a communication means
used for communication between the charge apparatus and the
application apparatus and the communication means transmits a
signal for controlling the switching device.
[0014] The battery pack is used as a power source for a motor of a
power tool.
[0015] According to the embodiment, it is possible to surely
protect a secondary battery even in a compact shape by limiting or
interrupting an overcurrent that flows during an overload such as
when the motor of a power tool is locked. According to the
embodiment of the present application, during recovery from an
abnormal state (overload) to a successful state, a shift to the
normal state is performed to enable reuse. Accordingly, it is
possible to set an area in which a protective operation is enabled
within an area in which damage to the battery cell by an
overcurrent is reliably prevented.
[0016] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 is a block diagram showing a schematic structure of
an electric screwdriver to which an embodiment is applicable.
[0018] FIG. 2 is a connection diagram of an embodiment of a battery
pack according to an embodiment.
[0019] FIGS. 3A to 3D are schematic diagrams used to describe a
thermostat with a PTC according to the embodiment.
[0020] FIG. 4 is a schematic diagram showing an example of
characteristics of the thermostat with a PTC according to the
embodiment.
[0021] FIG. 5 is a connection diagram showing protective operation
against an overcharge according to the embodiment.
[0022] FIG. 6 is a connection diagram showing protective operation
against an excessive overcharge according to the embodiment.
[0023] FIG. 7 is a connection diagram showing protective operation
against an excessive overcharge according to the embodiment.
[0024] FIG. 8 is a connection diagram showing protective operation
against an overcurrent according to the embodiment.
DETAILED DESCRIPTION
[0025] An embodiment will now be described in the following
order.
[0026] <1. Embodiment>
[0027] <2. Modification>
[0028] The following embodiment is a preferred specific example of
the present application, on which various preferable limitations
are imposed. However, the scope of the present application is not
limited by the embodiment unless limitations to the present
application are otherwise described.
1. Embodiment
[0029] "Example of a Power Tool"
[0030] An example of an electric screwdriver, which is a power tool
to which the present application is applicable, will be
schematically described with reference to FIG. 1. An electric
screwdriver 1 incorporates a motor 3 such as a DC motor in its
body. The rotation of the motor 3 is transferred to a shaft 4 and
the shaft 4 turns screws. A trigger switch 2 is disposed on the
electric screwdriver 1.
[0031] The electric screwdriver 1 has a battery pack 5 and a motor
control unit 6 in the lower part of the handle. The engaging
members (not shown) of the battery pack and the electric
screwdriver 1 are engaged with each other. As described later, each
of the battery pack 5 and the motor control unit 6 has a
microcomputer. The battery pack 5 supplies battery power to the
motor control unit 6 and the two microcomputers communicate with
each other. The battery pack 5 of the electric screwdriver 1 is
detachable and is attached to a charging unit when it is
charged.
[0032] The motor control unit 6 controls the rotation/stop and the
rotation direction of the motor 3. In addition, it interrupts power
supplied to the load during an over-discharge. The trigger switch 2
is placed between the motor 3 and the motor control unit 6; when
the operator presses the trigger switch 2, power is supplied to the
motor 3 and the motor 3 turns. When the operator puts the trigger
switch 2 in the original position, the motor 3 stops turning.
[0033] "Structure of the Circuit of the Battery Pack"
[0034] The battery pack 5 is configured as shown in FIG. 2. In the
battery pack 5, battery cells BT1, BT2, BT3, BT4, and BT5 (these
battery cells are collectively called the battery cell BT when it
is not necessary to identify these cells individually) of a
secondary battery such as a lithium ion secondary battery are
connected in series. If the full charge voltage of each battery
cell is 4.2 V, the full charge voltage of the battery pack 5
according to the embodiment is 21 V.
[0035] The positive side of the battery cell BT is connected to the
positive power terminal via the thermostat 12 with a PTC, which is
a current control device, and the negative side of the battery cell
BT is connected to the negative side power terminal via a resistor
13. Each voltage of the battery cell BT is measured by a control IC
(integrated circuit) 11. The control IC 11 measures the charge
current and discharge current of the battery cell BT. The voltage
and current are automatically measured at predetermined intervals.
A fuse 14 (for example, a chemical fuse) is placed between the
positive side of the battery cell BT and a charge terminal TH.
[0036] A FET Q3, which is turned on or off by the microcomputer 16,
is connected to a control terminal of the fuse 14. During an
excessive overcharge, a signal from the output terminal of the
control IC 11, that is connected to a resistor R4, is supplied to
the microcomputer 16, the FET Q3 is turned on, and the fuse 14
blows.
[0037] A regulator 15 is disposed to form a stable direct voltage
from the voltage of the battery cell BT. The output voltage of the
regulator 15 is supplied to the microcomputer 16 and the control IC
11 and is output to a terminal Vcc. The negative side of the
battery cell BT is connected to a terminal GND. Resistors R1 and R2
connected in series are placed between the positive side of the
battery cell BT and the terminal GND and the voltage of the
connection point between the resistors R1 and R2 is supplied to the
microcomputer 16.
[0038] A resistor R3 and FET Q1 connected in series and the
resistor R3 and a FET Q2 connected in series are placed between an
output terminal of the regulator 15 and the terminal GND. The FETs
Q1 and Q2 are turned on or off by the control IC 11. The FETs Q1,
Q2, and Q3 are, for example, N-channel FETs. The FET Q1 is turned
on by an overcharge detection signal output by the control IC 11.
The FET Q2 is turned on by an over-discharge detection signal
output by the control IC 11. The microcomputer 16 normally operates
in a sleep state to save power consumption and shifts from the
sleep state to a normal operation state when receiving a signal
from the control IC 11.
[0039] The above battery pack 5 is attached to, for example, a
charging unit (not shown) when it is charged and the microcomputer
16 in the battery pack 5 and the microcomputer in the charging unit
communicate with each other via the terminal Vcc, a data
communication terminal COM, and the terminal GND. When the battery
pack 5 is attached to the electric screwdriver 1, the microcomputer
16 communicates with the microcomputer in the motor control unit 6
of the electric screwdriver 1.
[0040] During charging of the battery pack 5 where it is connected
to the charging unit, certification is performed between the
battery pack 5 and the charging unit. In the certification, for
example, whether the battery pack and charging unit are authorized
is checked. The certification is preferably performed for each cell
of the battery pack 5. If certification is given, the same charging
operation as in normal lithium ion batteries is performed by the
charging unit.
[0041] During a discharge where the battery pack 5 is connected to
an application apparatus such as a power tool, a signal is received
or transmitted between the power tool and the battery pack 5. The
signal is used to confirm the successful state and confirm that the
voltage of the battery cell BT of the battery pack 5 is equal to or
larger than a certain voltage. When the voltage is equal to or
larger than the certain voltage, a discharge from the battery pack
5 starts.
[0042] "Thermostat with a PTC"
[0043] As shown in FIGS. 3A to 3D, the thermostat 12 with a PTC has
a movable contact 21 and a fixed contact 22. The movable contact 21
is secured to a movable end of a bimetal 23. The fixed end of the
bimetal 23 is secured to an input terminal 24. The bimetal 23 is
created by combining two metal plates with different coefficients
of thermal expansion and bends at a high temperature. The fixed
contact 22 is secured to an output terminal 25. The structure in
which the bimetal 23 is used to keep the contacts 21 and 22 in
contact or away from each other is referred to as a thermostat. A
PTC device 27, which is a positive temperature coefficient device,
is disposed between a conductive supporting plate 26 connected to
the input terminal 24 and a conductive supporting plate 28
connected to the output terminal 25. That is, between the input
terminal 24 and the output terminal 25, there are a current path
that goes through the thermostat including the bimetal 23 and a
current path that goes through the PTC device 27 in parallel.
[0044] The outside shape of the thermostat 12 (not shown) with a
PTC is a bar with a trapezoidal cross-section. Each of the battery
cells BT1 to BT5 is a cylindrical lithium ion battery and these
battery cells are tightly arranged to form a plane. The thermostat
12 with a PTC is placed in the space (valley) between adjacent
batteries. As a result, even when the thermostat 12 with a PTC is
used, it is possible to prevent the size of the battery pack from
exceeding the cell hold size.
[0045] This type of thermostat 12 with a PTC will be described
below. In the normal discharge state (or charge state), the
resistance of the bimetal 23 is much smaller than that of the PTC
device 27, so current flows through the bimetal 23. If an
overcurrent I1 flows through thermostat 12 with a PTC as shown in
FIG. 3A due to a lock of the motor, the bimetal 23 produces heat
due to the overcurrent I1.
[0046] As shown in FIG. 3B, the bimetal 23 bends due to the
produced heat and the movable contact 21 and the fixed contact 22
start separating from each other. If an overcurrent flows in this
state, an arc discharge occurs between the contacts 21 and 22,
possibly causing these contacts to be welded each other. However,
when the contacts start separating from each other, a most part I2
of the overcurrent passes through the PTC device 27, which has a
lower resistance, so the arc discharge is suppressed.
[0047] As shown in FIG. 3C, when the contacts are completely opened
due to a bend of bimetal 23, the PTC device 27 produces heat due to
the overcurrent I2 and the resistance of the PTC device 27 becomes
higher. As a result, a current that flows through the PTC device 27
is limited or interrupted. A small leak current usually flows
through the PTC device 27. As long as the overcurrent flows, the
PTC device 27 maintains a high resistance and the bimetal 23
remains bent due to heat produced by the PTC device 27. If the PTC
device 27 is not disposed, the contacts are opened and closed
repeatedly due to changes in temperature, possibly causing
chattering.
[0048] If the overcurrent is lost and a normal current I3 flows as
shown in FIG. 3D, the temperature of the PTC device 27 is lowered
and the resistance of the PTC device 27 is reduced. As a result, a
bend of the bimetal 23 is released and the contacts 21 and 22 are
placed in mutual contact. The normal current I3 flows through the
bimetal 23 that has a sufficiently low resistance. As described
above, this thermostat can not only interrupt an overcurrent but
also achieve a return to the normal state.
[0049] "Optimization of the Thermostat with a PTC"
[0050] The lead electrode and separator of a battery cell are
damaged when the amount of heat, which is defined by the product of
the current value of an overcurrent and the time period in which
the overcurrent flows, is large. The characteristics of the
thermostat 12 with a PTC, which limits an overcurrent to prevent
damage to the battery cell BT, can be determined on the basis of
the results of measurement in which a plurality of samples of
actually used battery cells are used. That is, many samples of
battery cells are prepared, and whether each of the samples is
damaged is checked by changing the discharge current and discharge
time for each of the samples. It is preferable to check damage
after performing a plurality of discharges.
[0051] FIG. 4 is an example of an overload damage map for the
lithium ion secondary battery (for example, a cylindrical type),
obtained from the above measurement result. The horizontal axis
indicates the discharge current (A) and the horizontal axis
indicates the discharge time (second). The curve 31 indicates the
case where the discharge rate is 100%. The area 41 inside the
dotted curve 32 is a non-damage area. The area 42 between the
dotted curve 32 and the dotted curve 33 is the area in which the
battery cell may be damaged. For example, this area is a separator
shrink area in which the separator of the battery cell shrinks. An
area 43 between the dotted curve 33 and the curve 31 is the area in
which the battery cell is damaged. For example, this area is a
separator melt area in which the separator of the battery cell
melts.
[0052] The thermostat 12 with a PTC limits an overcurrent by
bending the bimetal 23 and (separation between contacts) and
increasing the resistance of the PTC device 27, as described above.
That is, there is an interruption time from the timing at which an
overcurrent starts flowing to the timing at which an overcurrent is
limited to a level lower enough for the overcurrent to give no
effects. In consideration of variations in measurement, the
characteristics of the interruption time of the thermostat 12 with
a PTC are set so as to achieve "the characteristics of discharge
current versus discharge time" indicated by the curve 34 placed
slightly lower than the dotted curve 32 in FIG. 4. The dotted line
32 defines the border between the non-damage area 41 and the
separator shrink area 42, so damage to the battery cell can be
prevented by the characteristics of the curve 34. The setting of
the interruption time of the thermostat 12 with a PTC is possible
by setting the characteristics defined by the thickness etc. of the
bimetal 23 and the characteristics of the PTC device 27.
[0053] "Protective Operation"
[0054] In the embodiment, based on the measurement results of the
voltage and current detected by the control IC 11, protective
operation for protecting the battery cell BT from an overcharge,
over-discharge, and overcurrent is performed. Protective operation
against an overcharge will be described with reference to FIG. 5.
The overcharge detection voltage of the battery cell BT is
determined as, for example, 4.2 V.+-.0.5 V. If the control IC 11
detects that the voltages of the battery cells BT2 to BT5 are 4.1 V
and the voltage of the battery cell BT1 is 4.4 V, the FET Q1 is
turned on by an output of the control IC 11.
[0055] The microcomputer 16 receives a change of the drain voltage
caused when the FET Q1 turns on and is notified of an overcurrent.
The microcomputer 16 sends data for instructing the interruption of
the charge current to the microcomputer in the charging unit via a
data communication terminal COM. The microcomputer in the charging
unit receives this data and enables a charge current interruption
switch in the charging unit. As a result, the charging current for
the battery pack 5 is interrupted
[0056] Next, protective operation against an extreme overcharge
(referred to below as an excessive overcharge) will be described
with reference to FIG. 6. For example, the control IC 11 detects
that the voltages of the battery cells BT1 and BT3 to BT5 are 4.1 V
and the voltage of the battery cell BT2 is 4.5 V. The control IC 11
detects an excessive overcharge and supplies an excessive
overcharge detection signal to the microcomputer 16. The FET Q3 is
turned on by an output from the microcomputer 16. An excessive
overcharge is a permanent failure mode; the fuse 14 flows when the
FET Q3 turns on. The battery pack 5 having the blown fuse 14 is a
disabled product, which is unavailable.
[0057] Next, protective operation against an over-discharge will be
described with reference to FIG. 7. The control IC 11 detects that
the voltage of any of the battery cells BT1 to BT5 is equal to or
lower than an over-discharge detection voltage. The over-discharge
detection voltage is specified as, for example, 2.4 V.+-.0.1 V. For
example, the control IC 11 detects that the voltages of the battery
cells BT1 to BT4 are 2.8 V and the voltage of the battery cell BT5
is 1.6 V. The FET Q2 is turned on by an output from the control IC
11.
[0058] The microcomputer 16 receives a change of the drain voltage
caused when the FET Q2 turns on and is notified of an
over-discharge. The microcomputer 16 sends data or a signal for
instructing the interruption of the discharge current to the
microcomputer in the motor control unit 6 of the electric
screwdriver 1 via the data communication terminal COM. The
microcomputer in the motor control unit 6 receives this data or
signal and enables a discharge current interruption switch in the
motor control unit 6 to interrupt the discharge current.
[0059] Next, the rotation of the motor 3 of the electric
screwdriver 1 is locked, the same overcurrent (for example, 20 A)
as in a short-circuit of the coil is produced. Since the
characteristics of the thermostat 12 with a PTC are set as shown in
FIG. 4, the discharge current is limited by the thermostat 12 with
a PTC approximately 125 seconds after an overcurrent starts
flowing. FIG. 8 shows the limitation of the discharge current by
the thermostat 12 with a PTC. When the overcurrent stops flowing
and the temperature of the bimetal 23 is lowered, the contacts are
placed in mutual contact and a return to the normal state is made.
The fuse 14 is connected to a charge terminal TH and the charge
terminal TH is opened during discharging, so the fuse 14 does not
blow due to an overcurrent during discharging.
3. Modification
[0060] The embodiment is specifically described above, but the
present application is not limited to the above embodiment and
various modifications are allowed on the basis of technical ideas
of the present application. For example, a switching device (FET)
against an overcharge or over-discharge may be disposed within the
battery pack. In addition, a device with positive temperature
characteristics may be used instead of the PTC device. Battery
cells may be arranged in parallel or in series-parallel instead of
in series.
[0061] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *